1. Field of the Invention
The present invention relates to a storage control system and method for controlling the storage of data to the storage device.
2. Description of the Related Art
In a system handling large amount of data, such as database system in a data center, data is managed using a storage control system that is built separately from the host computer. This storage control system is a disk array system, such as a RAID Redundant Array of Independent/Inexpensive Disks), where many storage devices are enclosed in an array.
In such a storage control system, backup for copying data recorded in the storage device to another storage device is performed so that the data can be recovered even if the data recorded in the storage device become damaged. In this case, consistency of data must be guaranteed during the copying operation, because if the copied data is updated during the copying operation, a mismatch of data occurs, and the backup becomes meaningless.
A method for guaranteeing consistency of the backup data is to stop the program, besides the backup program, that access the data. But in case of a system for which high availability is required, programs cannot be stopped for a long time. Therefore it is necessary to provide a system that creates a stored image of the data at the point of the start of backup without interrupting the programs from updating data during backup. Hereafter the stored image of the data at a certain point in time is called “volume copy”, and the method which allows the system to update the data while having the volume copy of a specified point in time is called “volume copy management method”. Creating of a volume copy is called “volume copy acquisition”, and the data which is the target of volume copy acquisition is called “original data”. Stopping the status where the volume copy exists is called “volume copy deletion”.
One of the volume copy management methods is by duplicating data.
According to this method, for example, from a normal state where a volume copy is not acquired, a program on the storage control system creates all data on two storage areas (that is, data is duplicated). And the storage control system separates the two storage areas into individual storage areas, provides data existing on one storage area as original data, and provides the data existing on the other storage area as volume copy.
While the volume copy is acquired and duplication is being stopped (non-mirroring state), the storage control system enables update for the storage area of original data, and records the location of data update if a data update is generated. In the case of volume copy deletion, the storage control system restarts the duplication of the data, and copies the update data, of which content does not match between the two storage areas, from the storage area of the original data to the storage area provided as volume copy. This copying is called “mirror resynchronization”. In the case of volume copy deletion, the update data may be copied from the storage area of the volume copy to the storage area of the original data, which is the opposite of the above procedure, and such copying is called “reverse mirror resynchronization”.
The method of duplicating data by a program on a computer is shown in U.S. Pat. No. 5,051,887, for example.
As the storage device, a disk device (e.g. hard disk drive), magnetic tape storage device, or any other form of physical storage device can be used. Disk devices include high reliability high performance disk devices which are expensive but which have high reliability and performance, and low reliability low performance disk devices which are inexpensive but which have a lower reliability and performance than high reliability high performance disk devices. An example of a high reliability high performance device is a disk device having a fiber channel (hereafter “FC disk device”) interface, for which is being standardized by ANSI T11. An example of a low reliability low performance disk device is a disk device having an interface which is different from the interface of a high reliability high performance disk device, such as a disk device having an ATA (AT Attachment) interface (hereafter “ATA disk device), for which is being standardized by ANSI T13.
In the case of volume copy acquisition, the user may wish to store the original data in the storage area of the FC disk device (hereafter “FC storage area”), but may also wish to store the volume copy on the storage area of the ATA disk device (hereafter “ATA storage area”) because of the cost difference.
If the original data on the FC storage area and the volume copy on the ATA storage area are duplicated and used (that is, the FC storage area and the ATA storage area are in a paired status) to meet the above demand, the I/O processing performance (e.g. read or write speed of data) between the storage control system and the host device will drop, for example, when an I/O request (input/output request) is received from the host device to the storage control system and then processed, because the I/O processing performance of the FC disk device becomes equivalent to the ATA disk device. Also the performance of the ATA disk device becomes a bottleneck when the volume copy is acquired or when mirror resynchronization is performed.
Such problems could occur when the attribute levels of the data write destination storage devices, such as performance or reliability, are apart.